1. Field of the Invention
This invention relates broadly to the field of optoelectronics devices, and, more particularly to mechanisms that provide temporal delay to an electrical pulse and/or optical pulse and systems employing such mechanisms. In addition, the invention relates broadly to the field of semiconductor heterojunction devices, and more particularly, to transistors, optical emitters, optical detectors, optical modulators, optical amplifiers and other optoelectronic devices utilizing semiconductor heterojunction devices.
2. State of the Art
Mechanisms that impart a temporal delay to an optical pulse and/or electrical pulse are important components in many diverse applications, including optical/electrical clock generators and other frequency synthesis applications, optical/electrical communication systems, signal processing systems, and phased array antenna systems.
In optical applications, temporal delay of an optical pulse (referred to below as an input optical pulse) is typically provided in the electrical domain by converting the optical signal to an electrical signal using a photodetector. The electrical output of the photodetector produces an electrical pulse corresponding to the input optical pulse. A delay is imparted on the electrical pulse with a microstrip or stripline delay line. The length of the delay line dictates the temporal delay imparted on the electrical pulse. The electrical signal produced by the delay line is then used to drive a laser diode (or other optical source) to produce an optical signal that includes an output optical pulse that is temporally delayed with respect to the input optical pulse.
Temporal delay of an optical pulse can also be provided in the optical domain utilizing an optical delay line wherein path length of the optical delay line dictates the temporal delay imparted on the input optical pulse. Variable temporal delay is typically implemented by varying optical path length of the optical signal passing through the optical delay line. Path length variation can be realized with a multitude of optical fibers and a switch (such as a micromechanical mirror (MEM) switch) that switches the optical signal to one of the fibers to set the optical delay. U.S. patent application Publication US2002/0067877 describes an exemplary optical delay line utilizing this approach. Alternatively, path length variation can be realized by supplying the optical signals to a resonant cavity. Switchable mirrors enable the signal to resonate within the cavity (to increase the optical delay time) and escape the cavity for output. U.S. Pat. No. 6,028,693 describes an exemplary optical delay line utilizing this approach. It has also been proposed to use a photonic band gap structure (a plurality of layers which exhibit a series of photonic bandgaps) to provide variable optical delay. U.S. Pat. Nos. 6,396,617 and 5,751,466 describe an exemplary optical delay line utilizing this approach. In U.S. Pat. No. 5,751,466, the amount of delay is varied by applying a predetermined voltage or set of voltages (or by varying the frequency of the applied signal) to the layers of the photonic band gap structure to vary the index of refraction thereof.
In high frequency electrical applications, including RF and microwave communication/signal processing systems, temporal delay of an electrical pulse is typically provided by a microstrip or stripline delay line. The length of the delay line dictates the temporal delay imparted on the electrical pulse.
Each of these prior art approaches is costly to design and manufacture because it is complex and difficult to integrate with other optoelectronic devices (such as optical emitters, optical detectors, optical modulators, optical amplifiers), electronic devices (such as FET transistors and bipolar transistors), and optical devices such as passive optical waveguides.
Thus, there is a great need in the art for an improved optical/electrical pulse delay mechanism that provides accurate and controllable temporal delay and that has lower cost and ease of integration with a broad range of devices such as optical emitters, optical detectors, optical modulators, optical amplifiers, transistors, and passive waveguides.